In order to reduce the costs of solar energy generation in photovoltaic systems, it is desirable to make efficient use of the most expensive part of the system, namely the photovoltaic cell (for example, by providing increased current generation by using larger light fluxes). Conventionally, this is done by using large light-focusing solar concentrators.
For example, luminescent solar concentrators are used in connection with waveguides in this technical field. Basically, these luminescent concentrators consist of a large glass plate doped with fluorescent dye molecules. The dyes absorb light of specific wavelengths from the solar light incident upon it, and re-emit the light in all directions at longer wavelengths. A portion of this light is emitted within the critical angle of the supporting waveguide and is totally internally reflected and transported to the photovoltaic module of the photovoltaic system.
However, these luminescent concentrators presently show poor efficiency originating from a high re-absorption of the emitted light, from a poor efficiency of coupling light into the waveguide and from a poor efficiency in keeping the light within the waveguide.
Currently, there is a large worldwide research activity dealing with improvements of luminescent solar energy concentrators. Such current concentrators usually consist of a matrix in which luminescent materials are applied. Incident solar light is downconverted in a luminescent process as soon as it reaches the luminescent material and can then be used in a photovoltaic module.
However, again re-absorption of converted light strongly contributes to energy losses in these luminescent concentrators. The optical gain factors (ratio of incident light intensity and light intensity received by the photovoltaic module) that can be achieved are limited by these re-absorption effects. With respect to the current luminescent concentrators, re-absorption effects occur in the luminescent materials, and additionally the matrix itself may also negatively affect the optical gain factors by optical absorption in the matrix.